In recent years, organic light-emitting devices including a display unit such as a FPD (Flat Panel Display) and a lighting unit such as a lamp are developed for practical applications using an organic EL (Electroluminescence) element. In the organic EL element, an organic EL layer including an organic light-emitting layer is interposed between a pair of mutually opposing electrodes. The organic EL layer emits light when a voltage is applied between the electrodes to allow an electric current to flow through the organic EL layer. With a view to obtain increased brightness, there is recently proposed a structure called a Multi Photon Emission (MPE) in which organic EL layers are formed one above another with a charge generation layer interposed therebetween.
When an organic EL device (hereinafter, the term “organic EL Device” is also used interchangeably to refer to an “OLED (Organic Light Emitting Diode)”) is used for a lighting apparatus, an MPE structure is suitable for increasing brightness and lifespan. In the MPE structure, an organic layer is formed thick, and thus the costs grow higher. This is because the MPE structure is optimized in a single unit structure and the thickness of the organic layer is finely adjusted by layering individual units one above another. As a matter of course, simulation results are also utilized. It is however the basic design concept that the single unit structure is optimal.
In the conventional organic EL device having the MPE structure, there is a desire to reduce manufacture cost by saving material cost based on mass production.